Which gaming platform first introduced a player-to-player marketplace that allowed users to trade virtual items for real money, establishing a groundbreaking e-commerce model in gaming?

The gaming industry has evolved dramatically in how virtual goods are bought and sold. In-game economies have become sophisticated ecosystems with their own marketplaces, currencies, and economic principles. This trivia question focuses on a pivotal moment in gaming e-commerce history that changed how players interact with virtual goods and shaped future retail innovations in the gaming space.

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Second Life (Linden Lab)
World of Warcraft (Blizzard)
EverQuest (Sony Online Entertainment)
Counter-Strike (Valve)